From October 1991 through March 1992, the NASA ER-2 and the DC-8 aircraft were flown out of Fairbanks, Alaska, and Bangor, Maine, to examine the evolution of the chemistry of the stratospheric polar vortex over the course of the winter. This was AASE II.

AASE II began about two and a half years after the Airborne Arctic Stratospheric Experiment (AASE), which determined that the chlorine chemistry in the Northern Hemisphere polar winter stratosphere was indeed perturbed, similar to the situation in the Southern Hemisphere winter. This mission was designed to measure chemical and meteorological variables as the Northern polar vortex--the ring of winds which circles the pole in winter--evolved through the season.

The first deployment was out of Fairbanks, Alaska, in October 1991. The ER-2 flew north to the pole to survey the beginnings of the polar vortex. Subsequent deployments were staged from Bangor, Maine, for two-week periods spaced about two weeks apart from November 1991 through March 1992. Most flights were north towards the polar vortex, but a few went south towards the tropics to survey aerosols injected into the stratosphere by the eruption of the Pinatubo volcano in June 1991.

The ER-2 was joined by the NASA DC-8 beginning with the January deployment. The DC-8, which has a much longer range than the ER-2, flew circuits from NASA Ames Research Center in Moffett Field, California, to Fairbanks, Alaska, to Stavanger, Norway, to Bangor, Maine, and then back to NASA Ames.